LTC2913 datasheet(15/24 Pages) LINER

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LT4363

4363fa

CTMR

0.1µF

RSNS

10m

IRLR2908

VIN

12V

VOUT

12V, 3A

CLAMPED

AT 16V

4363 F06

LT4363DE-2

GND

TMR

OUT

SNS

SHDN

VCC

FLT

ENOUT

47nF

D1*

SMAJ58CA

4.99k

57.6k

GATE

10k

2N3904

1N4148

*DIODES INC.

APPLICATIONS INFORMATION

Figure 6. Overvoltage Regulator with N-channel MOSFET

Reverse Input Protection

Figure 5. External GATE network

Limiting Inrush Current and GATE Pin Compensation

TheLT4363limitstheinrushcurrenttoanyloadcapacitance

by controlling the GATE pin voltage slew rate. An external

capacitorcanbeconnectedfromGATEtogroundtoreduce

the inrush current at the expense of slower turn-off time.

The gate capacitor is set at:

IGATE(UP)

IINRUSH

• CL

The LT4363 does not need extra compensation compo-

nents at the GATE pin for stability during an overvoltage or

overcurrent event. With transient input voltage slew rates

faster than 5V/µs, a gate capacitor, C1, to ground is needed

to prevent self enhancement of the N-channel MOSFET.

The extra gate capacitance slows down the turn off time

during fault conditions and may allow excessive current

duringanoutputshortevent.Anextraresistor,R1,inseries

with the gate capacitor can improve the turn off time. A

diode, D1, should be placed across R1 with the cathode

connected to C1 as shown in Figure 5.

threshold during a fault. The pass transistor is not allowed

toturnbackonevenafterthecooldownperiodhasfinished.

This prevents the pass transistor from cycling between ON

and OFF states when the input voltage stays at an elevated

level for a long period of time, reducing the stress on the

N-channel MOSFET. For the latch-off version, LT4363-1,

the overvoltage comparator function is not available.

Reverse Input Protection

A blocking diode is commonly employed to protect the

load when reverse input is possible, such as in automo-

tive applications. This diode causes extra power loss,

generates heat, and reduces the available supply voltage

range. During cold crank, the extra voltage drop across

the diode is particularly undesirable.

The LT4363 is designed to withstand reverse voltage with-

out damage to itself. The VCC, SHDN, UV, and OV pins can

withstandupto60VofDCvoltagebelowtheGNDpotential.

Back-to-back MOSFETs must be used to block the current

path through Q1’s body diode (Figure 6). Figure 7 shows

the approach with a P-channel MOSFET in place of Q2.

4363 F05

LT4363

GATE

IN4148W

Undervoltage/Overvoltage Comparators

The LT4363 has both undervoltage and overvoltage com-

parators that can be used to sense the input supply volt-

age. When the voltage at the UV pin is below the 1.275V

threshold, the GATE pin is held low to keep the external

MOSFET off. The supply voltage at the VCC pin should be

at least 4V for the UV comparator to function.

The overvoltage comparator prevents the LT4363-2 from

restarting if the voltage at the OV pin is above the 1.275V

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